Field of the Invention
The invention relates to a method for producing a product having an uneven microstructure on a surface thereof.
Description of Related Art
In recent years, it is known that the products with the uneven microstructure on a surface thereof present antireflection effects, lotus effects and the like, whereas the period of the uneven microstructure is equal to or less than the wavelength of visible light. Particularly, because refractive indices keep increasing continuously from the refractive index of the air to the refractive index of the product, the uneven structure that is constructed with slightly convex cone structures, so-called the moth-eye-structure, becomes an effective antireflection means.
The method of forming the uneven microstructure on the surface of the product arouses interest, which is performed by inserting a liquid active energy ray curable resin composition between a substrate and a mold having a surface with the uneven microstructure thereon, and irradiating with an active energy ray for curing the active energy ray curable resin composition to form a cured resin layer, onto which the uneven microstructure is transferred, on the surface of the substrate.
Furthermore, a mold, which has anodized aluminum with multiple pores on a surface of an aluminum substrate and is used as the aforementioned mold, is of interest because the mold can be easily manufactured (Patent literature No. 1).
However, based on the following reasons (i)-(iii), a contact interface between the active energy ray curable resin composition and the aforementioned mold is significantly increased, and consequently it is difficult to release the mold from the cured resin layer.
(i) The average interval between the pores of the anodized aluminum is about 100 nm, and the distance between the closest portions of the adjacent pores ranges from several nanometers to tens nanometers. That is, the structure is very fine.
(ii) As described in Patent literature No. 1, when etching and anodizing are repeatedly performed to form the pores, the smoothness of walls of the pores decreases and the walls of the pores may be roughened to some extent.
(iii) If attempted to obtain functions such as sufficient antireflection effect, the aspect ratio of the pores needs to be relatively enlarged.
As a method for improving the releasability of the cured resin layer and the mold, a method is proposed to treat the surface of the mold, on which the uneven microstructure is formed, with a release agent (external release agent) having a functional group (B) capable of reacting with a functional group (A) existing on the surface (Patent literature No. 2).
However, the above-mentioned method has the following problems (iv) and (v).
(iv) If the uneven microstructure of the mold is transferred repeatedly, the external release agent is peeled off from the surface of the mold, and the releasability between the cured resin layer and the mold is lowered gradually. As the releasability between the cured resin layer and the mold decreases, the productivity of the product also declines. Moreover, a portion of the transferred uneven microstructure is damaged, and the transfer accuracy of the uneven microstructure is reduced.
(v) The external release agent peeled off from the surface of the mold is transited to the surface of the product and contaminates the surface of the product. The contamination may last for a period of time starting from the beginning of the transfer (until repetitively transferring for several hundred times, for example). Therefore, products, which are obtained during the period from the beginning of the transfer until the products have less surface contamination and have stabilized surface property, cannot be sold. The raw materials or ingredients that are consumed before the surface property of the products becomes stabilized are wasted.